Turbofan engines are well known. They are typically composed of a fan driven at the front of the engine that draws air rearwardly through a by-pass duct that is defined by the core engine cowling and by the fan cowling spaced outwardly from the core cowling. In the case of a short nacelle, i.e., a separate flows nacelle, the generally annular duct that is bounded by the inner core cowling and the outer fan cowling, channels the by pass flow only while the core flow is channeled by the core nozzle inwardly installed to the core cowling. In the case of a long nacelle, i.e., a confluent flows nacelle, the upstream portion of said annular duct channels the by-pass flow only and its downstream portion channels the by-pass flow and the engine core flow.
Landing speeds of modern aircraft being typically high, it is of great importance to assist the wheel braking for the deceleration of the aircraft by enhancing its stopping capability using aerodynamics means. Aerodynamics decelerating means have a positive economic impact in helping reduce the wear on the wheel brakes but more important contribute to enhancing the aircraft safety at landing on wet or icy runways. However, since thrust reversers are only used approximately 30 seconds of the flight, it is essential that said reversers be of light weight and simple so that the cruise performance and the operational characteristics of the aircraft are not affected by the thrust reverser.
Thrust reversers being commonly used on aircraft are very well known. Generally speaking, they can be categorized into two categories. The first one called also fan reversers is the type of reversers that reverse the by-pass flow only and the second one the type that reverses the by-pass and the core flows. Since the second category leads to a more complex, a heavier structure and can only be installed on confluent flows engine, this type will not be considered in this invention.
The known prior art fan thrust reversers can be, generally speaking, categorized in three distinct types. First type consists in the aft axial translation of the by-pass structure for the deployment of a series of blocker doors inside the by-pass duct structure and the opening of an aperture in conjunction with the exposing of radial cascade vanes for redirecting the by-pass flow in the forward direction. The second type uses also the aft axial translation of the by-pass structure for closing the by-pass flow duct and opening of an aperture for re-directing the by-pass flow in the forward direction. Said aperture of prior art may or may not be equipped with cascades vanes. The second type differs from the first one, as the series of blocker doors is no longer present. The third type consists of doors that rotate inside the bypass flow and outside in the ambient air for re-directing the by-pass flow in the forward direction. This fan reverser type is generally called “petal” or “pivoting doors” reverser.
The drawbacks of the first type prior art fan reversers are the necessity to provide aft translation capability to two roughly symmetrical but distinct cowlings for reversing the fan flow, and the presence in the by-pass duct of links, known as drag links, for the deployment of the series of blocker doors. The drag links are degrading the engine performance in forward thrust, the blocker doors are increasing the complexity and the weight of the assembly and finally the required guiding, and sliding tracks for reverser operation of the two roughly symmetrical but distinct halves are significantly increasing the weight of the nacelle. Each of the two symmetrical halves forms a D-duct that is hinged on each side of the aircraft pylon. Each D-duct can be separately pivotally opened around its hinges, with a dedicated actuator per D-duct for maintenance access to the engine. When the D-ducts are closed and latched they are sized for reacting the required engine operational aerodynamic static pressure acting inside the D-ducts. This type of structural arrangement contributes to significantly increasing the overall weight of the assembly because of the structural discontinuity between the two halves. The D-duct configuration impacts weight, reliability, number of parts and cost.
While the second type of fan reverser appears to be an improvement, since the drag links and the associated series of blocker doors have been eliminated, its drawback is that it still necessitates the translation capability of two roughly symmetrical but distinct cowlings for reversing the fan flow. The previous described drawbacks are then still valid for this configuration. Typical cascade reverser of this type is disclosed in U.S. Pat. No. 6,438,942 and U.S. Pat. No. 6,568,172
Although the third type appears to be an improvement over the first and second types, its main drawback is the presence of wells in the by-pass duct for housing of the actuators that control the pivoting of the doors. The forward engine performance degradation that is associated to these wells usually requires additional flaps mechanism for fairing them. Other drawbacks of this type of fan reverser are the required large actuators stroke and the extensive protrusion of the pivoting doors in the ambient air when they are pivoted to their deployed position. The required large number of latches drives significantly the complexity of the system and control for this type of reverser.
In sum, the need has arisen for improved techniques for providing a low weight cascade fan reverser for a turbofan engine. Among other things, such techniques should provide for the elimination of D-ducts and/or blocker doors. Further, these techniques preferably optimize direct thrust performance of the engine and provide a clean aerodynamic boundary flow surface for the outer cowling of the by-pass duct. Additionally, the number of actuators of the reverser should be reduced for further weight and cost reduction and techniques found that allow the reverser assembly to be moved rearward for access to the engine.